Alliteration is a pattern in speech in which a series of words or stressed syllables begin with the same letter or sound. It is most commonly used in the Germanic poetic traditions, most notably Anglo-Saxon and Norse.
The conventions for alliteration can change subtly depending on the culture. In Norse poetry any two stressed syllables that begin with vowels are consider to alliterate. Modern English listeners however expect alliteration to relate only to words, and to have a more strict vowel alliteration. For instance "Evan's angry owl" would be considered to alliterate by Norse conventions, but not by modern English.